The present invention relates to reciprocable members and, more particularly, to reciprocable members such as valves with an anti-float arrangement.
Exhaust manifold pressure has historically been one of the major design constraints for engine brakes that limit engine braking power. This is especially the case on single-valve actuation engine brakes, where only one exhaust valve spring is available to control exhaust valve motion during engine braking. In combination with valvetrain acceleration in the ‘closing’ direction, high exhaust manifold pressure during engine braking can cause the valve to ‘float’, or not follow the cam profile over the closing flank of the valve lift profile, producing the potential of piston-to-valve contact, valve seat wear due to uncontrolled valve closing, and valvetrain damage due to impact stresses. Valve float can generally be thought of as meaning unintended, uncontrolled motion of the valve. In extreme cases, high exhaust manifold pressure spikes have been known to ‘blow’ the exhaust valves off their seats during the intake stroke, causing unintended valve lift and, again, uncontrolled valve seating. This invention is for the purpose of reducing or eliminating the influence of exhaust manifold pressure on valve float.
Problems with valve float are not limited to exhaust valves. In reciprocating members, generally, where different pressures might be present on different sides of a valve arranged to be alternately seated in and displaced from a valve seat, it occasionally happens that the valve is held in an open position or otherwise fails to seat properly in the valve seat (or, in some situations, is forced closed by gas pressure when it is intended to be open) because the pressure differential holds the valve in an open position against some mechanical structure such as a spring arrangement that would ordinarily urge the valve head to the closed position in the valve seat. Whatever the application, valve float can be problematic.
Solutions to problems with valve float such as valve heads being struck by pistons include desmodromic valves that are positively closed by a cam and leverage system. Disadvantages to such systems include their high service costs and frequent service requirements needed as the result of high precision requirements.
It is desirable to provide an exhaust valve arrangement that reduces problems with valve float. It is also desirable to provide a valve arrangement for use in other applications that can reduce problems with valve float. It is also desirable to provide a valve arrangement that can reduce problems with valve float with minimal extra cost and requiring minimal additional servicing.
In accordance with a first aspect of the present invention, a valve arrangement comprises a valve member comprising a valve stem and a valve head having a first and a second side on the valve stem, a wall between a first space and a second space, the first and second sides of the valve head facing the first and second spaces, respectively, an opening in the wall defining a valve seat, the valve member being movable between an open position in which the valve head is disposed in one of the first space and the second space and a closed position in which the valve head is disposed in the valves seat, and a piston mounted relative to the valve stem, the piston being disposed in a cylinder in flow communication with the first space.
In accordance with another aspect of the present invention, a spring loaded piston arrangement comprises a cylinder, a piston disposed in the cylinder, the piston being mounted on a stem, the stem having a spring retainer, and a resilient member in contact with the spring retainer and arranged to urge the spring retainer away from the piston.
In accordance with yet another aspect of the present invention, an exhaust valve arrangement comprises a cylinder having a top end, an exhaust conduit connected to the cylinder by an opening in the top end of the cylinder, the opening comprising a valve seat, a valve member comprising a valve stem and a valve head on the valve stem, the valve member being movable between a closed position in which the valve head is received in the valve seat and an open position in which the valve head is spaced from the valve seat, and a resilient member arranged to urge the valve member to a closed position. A piston is mounted relative to the valve stem, the piston being disposed in a second cylinder in flow communication with the exhaust conduit and arranged such that a change in pressure in the exhaust conduit changes a degree of compression of the resilient member.